In this regard, silica has long been used as a reinforcing filler in tread compounds. Silica is used instead of carbon black and together with special chemical substances (silanes) which interact with the silanol groups of silica to prevent its particles from forming hydrogen bonds. With the right functionality, silanes may also interact with the polymer base to form a chemical bridge between it and the silica. Silica is employed for the advantages it affords in terms of rolling resistance and wet-road-holding performance.
As is well known within the industry, compounds may be produced using synthetic polymers produced by solution or emulsion synthesis. And, as is known from patent literature, appropriate activators may be used at the non-productive stages to enhance reactivity between the silica, silane, and polymer (U.S. Pat. No. 5,580,919B).
Tests show that, in silica-containing compounds, in which the polymer base is produced by emulsion polymerization, activators produce little improvement in the reactivity of the silica/silane/polymer system, thus resulting in less than optimum rolling and abrasion resistance of the compound.
The same problems are also encountered when using a natural rubber polymer base.
A need is therefore felt for a method of producing compounds, in which the polymer base is composed partly of natural rubber or a polymer produced by emulsion polymerization, but without impairing the rolling and abrasion resistance characteristics of the compound.
The Applicant has surprisingly discovered a method of producing compounds at least partly containing natural rubber or polymers produced by emulsion polymerization, without incurring the drawbacks of the known art.
With respect to the known art, the method according to the present invention involves no additional ingredients and no increase in the amount of ingredients used, but simply alters the timing with which they are mixed. In fact, using too many ingredients would make it difficult to control the various target properties of the compound.